Phagocytosis and pinocytosis are active transport systems, both processes are examples of how a cell can move a substance through the plasma membrane into the cytoplasm and isolate it. Active transport systems move substances into cells up a concentration gradient.
Phagocytosis enables a cell to engulf foreign materias, usually solids. Leukocytes destroy bacteria by phagocytosis, they move the foreign material into the cell using energy provided by ATP. Once inside the cytoplasm lysosomes destroy the bacteria.
Pinocytosis is similar to phagocytosis except this process moves fluids into the cell rather than solids. Both processes rid the body of unwanted substances.